Control of optical-feedback-induced laser intensity noise in optical data recording

Semiconductor lasers are commonly used for storage and retrieval of information in optical data recording systems. A measure of the importance of this emerging optoelectronic technology is provided by the compact-disc players that have already penetrated the consumer electronics market. The same technique is now being extended to the mass storage devices capable of storing gigabytes of information on a single optical disk. Although optical disk-based mass storage devices are already available commercially, several technological problems must be solved to further improve their performance. One such problem is related to the control of relative intensity noise (RIN) of semiconductor lasers used inside the optical head for reading and writing the data to the optical disk. The RIN of a well-designed semiconductor laser isolated from external reflections is typically low"2 enough (<120 dB/Hz) so that it can be used successfully in optical data recording systems. Unfortunately, it is often the case that a small fraction of the laser output is invariably fed back into the semiconductor laser because of the reflection occuning at the disk surface. Figure 1 shows the schematic design of an optical head used for reading and writing the data to the optical disk. To minimize the optical feedback